The present invention relates to a process for hydrogenation of heavy oil and more particularly to a process for hydrogenation of heavy oil in which the recovery of oil from a catalyst slurry consisting of a used catalyst and product oil as withdrawn from a hydrogenation reactor is increased and thus the yield of product oil is high.
A method of hydrogenating hydrocarbons such as heavy oil by the use of a fine particle catalyst in which the catalyst slurry obtained by the hydrogenation is subjected to solid liquid separation by the use of a catalyst separator such as a centrifugal separator, a hydrocyclone, a filter and the like to separate the product oil and a used catalyst containing an oil fraction is regenerated by burning and recycled for reuse has been known as described in Japanese Patent Publication No. 11354/1982. The fine particle catalyst used in the above method has a large surface area as compared with a pelletized or tableted catalyst and, therefore, a reduction of catalytic activity due to deposition of carbon or metal is decreased and particularly a reduction of catalytic activity due to deposition of metal is effectively prevented. It is also known that the fine particle catalyst can be easily mixed with heavy oil and uniformly distributed in a reactor and furthermore the exchange of the catalyst in the reactor can be easily carried out in the slurry condition and, therefore, hydrogenation of heavy oil can be carried out stably over a long term. In order to carry out the stable reaction over a long term, however, it is necessary to supply a makeup catalyst of high activity or a regenerated catalyst, and further to withdraw the used catalyst. The used catalyst is withdrawn as a catalyst slurry along with the product oil. In the above method, however, the oil contained in the catalyst slurry is recovered only insufficiently.
When a solid/liquid separator such as a centrifugal separator and a hydrocyclone is used, although the recovery rate of the catalyst particles is high, it is necessary to limit the concentration of the catalyst in a cake discharged from the centrifugal separator or in the underflow of the hydrocyclone to 40 to 70% by weight in order to attain smooth flow of the cake or the underflow (Handbook of Chemical Engineering, Revised 4th Ed., edited by Kagaku Kogaku Kyokai, published by Maruzen Co., Ltd., Japan, pp. 1070-1071). In other words, the fluid, e.g., cake discharged from the centrifugal separator or underflow of the hydrocyclone, contains 30 to 60% by weight of product oil but not recovered. This oil is burned in the presence of oxygen at the subsequent catalyst oxidation regeneration step and cannot be recovered, leading to a decrease in the yield of product oil.
That is, in the conventional suspension bed-type hydrogenation process using a powdery catalyst, the recovery and regeneration of the catalyst particle is sufficiently satisfactory, but the recovery of product oil entrained by the catalyst particle is not sufficiently high and the yield of product oil is low.